Electronic publishing

ABSTRACT

A novel electronic printing system for operating both a linear-raster electro-optical display device and a linear-raster type printer, which system is capable of integrating alphanumeric and/or graphics information and gray-scale or picture information, all on a single data base from which one may either (or both) print the data out on the printer as images, or display the data on the display device as images. The system includes look-up tables storing respective first and second subsets of a set of substantially disjoint multiple-bit binary index numbers. Each of the numbers of the first subset represent information corresponding to a respective gray-scale density level rendered as a respective matrix of points forming a corresponding gray-scale cell to be printed by the printer. Each of the numbers of the second subset represent information corresponding to a unique shape of an edge rendered as a respective matrix of points to be printed by the printer. Means are provided for translating an image of the information to be printed and/or displayed into an array of index numbers selected from the subsets, and for storing that array. Conversion means are provided for converting at least a major portion of the array into electrical signals for forming a display of substantially the desired image on the display device and for converting at least a major portion of the array into electrical signals for forming matrices for assemblage as the image in printed form on the printer.

This invention relates to electronic publishing, a technology employingelectronic means for creating, storing, revising, transmitting andon-demand printing of documentation.

Many companies, particularly those engaged in highly technical productdevelopment and sales, have many product lines and products in theirbusiness portfolios. An exceedingly large number of different documentsneeded to support each product may have to be kept on hand. A continuousflow of requests for such documents tend to be constantly received fromprospects, customers, field salesmen, international sales, customertraining, distributors, and service. Literature shortages that delay thefulfilling of such document requests may result in poor field morale,unhappy customers, and, ultimately, lost business. A hiatus in supply,for example of instruction manuals, may result in late shipments anddelayed or even diminished revenues.

If document shortages, and the problems they cause, are to be avoided,printed material should be treated in the same manner as manufacturinginventory. As new documents are printed, they should go throughreceiving, be inspected, sent to the literature distribution room,logged into the literature inventory, and placed in an assigned shelfspace. To know when it is time to reorder, either a continuous inventoryshould be maintained by logging each piece of literature as it is sentout or, alternatively, reorder points must be established and periodicinventories need be taken. The costs of inventorying product supportdocumentation, including the not insignificant cost of the space takenup by the material, can be quite high. In addition, one must alsoconsider the cost of keeping artworks, photographs, flats, printer'snegatives and the like on file to allow documents to be revised andreprinted.

A company's literature frequently needs revision because productspecifications tend to change, engineering revisions are often made onexisting products and must be communicated to field service personnel,new applications for products arise and need to be documented for thefield sales force, and mistakes found in instruction manuals have to becorrected. Since it is almost impossible to predict when a particulardocument will require revision, it is difficult to estimate how manyshould be printed at any time. Although the cost per copy of printinggoes down as the press run goes up, ordering a large press run riskshaving the savings wiped out when a revision necessitates scrappingliterature. Too small a press run means an excessively high piece price,plus the price of reordering and reinventorying. Even with the best ofplanning, unanticipated revisions obsolete a significant fraction of theliterature inventory.

A company may either set up an in-house printing facility or send itsprinting to outside shops. Inhouse facilities require additional trainedpersonnel, space and management time. Outside printing requiresadditional scheduling, obtaining competitive bids, issuing of purchaseorders, inspecting incoming material for quantity and quality, androuting the material to the literature inventory room.

The preparation of technical support documentation by conventionalmethods without electronic publishing, may require considerable effortand coordination among a large number of individuals such as engineers,writers, photographers, designers, typesetters and printers. Writersmust work, often hand in hand with technical personnel such as engineersand scientists, to produce technically accurate copy. Illustrators maybe needed to make drawings and diagrams, or photographers may beretained to produce photographs to be included in the copy. The documentmust be laid out. Copy needs to be typeset and proofread against theoriginal text. Drawings may be photostatted to size and pasted-up toproduce artwork for the printer. Using a special camera, the printerusually produces negatives that are used to make proofs which must beexamined for mistakes in paste-up and for imperfections in the art workor film. The reproduction of photographs also involves cropping, sizingand converting the photograph into half-tone negatives for conversion toprinting plates. Only when all of these steps, and possibly many others,are completed, may printing actually begin.

To circumvent the many problems encountered when documents are providedby conventional means, digital computer-controlled electronic devices,known as electronic publishing systems, are being increasingly used inthe preparation, revision, storage and printing of documentation. Suchpublishing systems should be capable of handling documents containingall of the various categories of printed materials such as anycombination of typographic characters, line art and continuous tonepictures. As used herein, the term "typographic characters" is intendedto include, but not be limited to, letters of alphabets (e.g Roman,Russian, Greek, Arabic, Armenian and Kanji), ideographs (e.g. Chineseand Japanese), numbers, punctuation marks and accents, and mathematicaland scientific symbols, in any and all fonts, point sizes and spacing.As used herein, the term "line art" is intended to include a variety oflines-on-plane images such as graphs, charts, engineering drawings,schematics, outline sketches and the lixe. The term, "pictures" refersto continuous tone images, such as photographs, frames of video,half-tone reproductions and the like.

Electronic publishing systems typically comprise mass storage means ormemory for electronic storage of information, a workstation for the userto provide input data and instructions for the creation and revision ofdocuments, an appropriately programmed digital host computer, andelectronic printing means for printing documents in accordance withelectrical signals provided by the computer. The term "electronicprinting", as used herein, includes means for producing, under computercontrol, plain paper hardcopy or reproduction masters, e.g. printingplates, photosensitive paper, film or like materials. An important typeof printing device, particularly useful in the present invention, is ahorizontal line-raster printer, (hereinafter simply referred to as aline-raster printer) e.g. typically one in which a light beam is adaptedto be (1) focussed to a small spot on a photosensitive surface, (2)intensity-modulated by an electrical signal, (3) rapidly deflected so asto sweep the spot along a first line between margins, and (4) returnedto the beginning margin with a small displacement normal to the sweepline so as to be positioned for sweeping along a second line parallel tothe first line. One type of such a line-raster printer, known as thelaser printer, employs a laser beam as the light beam, and forms aprintable image on a xerographic surface from which plain paper hardcopymay be produced by conventional xerographic techniques. Another categoryof line-raster printers, known as electronic typesetters, use a laserbeam or light from a fiber-optic cathode ray tube to produce a printableimage on photosensitive film. The film may be used to make printingplates for document reproduction on conventional letterpress or offsetpresses.

A typical workstation includes a high-resolution electrooptical imagingdevice, (e.g. 1000 to 2000 lines), typically a cathode ray tube (CRT)terminal for displaying images of the pages being created and revised; akeyboard for text entry and correction; and a screen-pointing andcontrol device such as a "mouse" or "trackball". The workstationeliminates the time-consuming paste-up of blocks of typeset text andgraphics onto flats, thereby simplifying preparation and revision ofdocuments. Through the agency of the workstation and the assistance ofthe host computer, documents can be created using a set of rules forpage layout, including such parameters as margin width, column width,type style or font, type size, line spacing and justification.

To create a document, the text intended to appear on a page is enteredinto the system either at the workstation or at a remote word-processingterminal linked to the system computer by a conventional communicationsline. A typeset version of the text is produced based on the key strokesand operator-selected choices of font, margins, column width and linespacing, thus permitting the operator to see a page image, i.e. apreview of how each page will look when printed, and permitsproof-reading and editing of the typeset text directly on the screen. Ata scale of one-to-one, the page image will be the same size as the pageto be printed, the individual characters appearing in the same size,typestyle and at the same coordinates as they will appear on the printedpage. Some systems also permit display of line drawings and othergraphic elements, as well as typographic characters.

Images of typographic characters, line art and other graphics are formedon the workstation screen from a series of display pixels (basic pictureelements) provided by control of the excitation of the tube phosphor ateach point on the display. The visual intensity of the phosphor pointsare controlled in a binary (i.e. on-off) manner by an electronicallystored array of single-digit binary numbers or bits, the array beingknown as a bit-map. Each number of the array corresponds to a pixel onthe screen, the rows of the arrays corresponding to the raster lines. Inmost systems, each raster line displayed on the CRT has a width orheight about equal to the pitch of the line, i.e. the spacing betweenraster lines, center to center. Each raster line is divided intosegments each of which constitutes a pixel, each segment beingdimensioned so that horizontal and vertical lines on the screen, whenone pixel wide, will have the same width. Thus, the resolution,expressed in pixels/inch, is typically the same as the pitch.

Similarly, a bit map may be used to carry out electronic printing on aline-raster printing device. In such instance, a series of small pixelsare electronically printed onto a substrate under the control of a bitmap, the printed matter being rendered with an intensity contrastingwith the substrate or background. While it is possible to drive aline-raster printing device with the same bit map used to generate thepage image on the CRT, this is not generally done because the printingis of inferior quality because of the relatively low resolution of thebit map.

While there are obvious economic advantages in using the screen bit mapto produce electronically printed pages, limitations in reasonable-cost,commercially-available technology limit CRT displays to about 2000 linesof resolution. On the other hand, even a relatively low-resolution,laser, line-raster printer with a resolution specification of 240 linesper inch (or 2,640 lines to output an 11-inch page) has a higherresolution than most high-resolution workstation screens. A 400 line perinch printer requires 4,400 lines to output a page, and a 1000 line perinch laser-to-film device requires 11,000 lines.

Thus, generally a second, higher resolution bit map is produced withinthe line-raster printing device from a series of commands and textstrings sent from the workstation to processing means in the line-rasterprinting device. Such processing means typically comprising amicroprocessor, memory and means for generating a bit map, uses digitaldescriptions of the various typographic characters stored in its memory,to build a bit map of greater detail than the one used to control thedisplay. The use of separate microprocessors and bit maps in the hostcomputer and the raster printing device increases the complexity andcost of the electronic publishing system.

It is desirable that electronic publishing systems be able to displayand print continuous-tone pictures such as photographs and frames ofvideo. Consequently, continuous-tone pictures are typically digitizedinto an array of numbers larger than one binary bit, wherein each numberor gray-scale pixel represents the level of gray at a point within theimage that has been sampled and expressed as a number. For example, anarray of two digit (or bit) binary numbers allows four levels of gray tobe displayed, whereas, eight-bit binary numbers or bytes, allow 256levels to be displayed. In practice, six-bit binary numbers (allowing 64levels of gray to be displayed) represent a good compromise betweenlimiting the size of the binary numbers used and maintaining the qualityof the image displayed. The use of less than six-bit numbers usuallycause the display of photographs and other gray-scale images to containcertain artifacts due to the different levels of gray within the pictureappearing as visible bands.

Several limitations of the bit-map displays makes the use of gray-scaledisplays preferable in electronic publishing systems. Bit map displaysare unable to display continuous-tone pictures and images except aslow-resolution dithered pictures, that is, crude images having thebrightness or darkness of relatively large local areas of the picturerepresented by differing numbers of on and off display pixels atdifferent areas of the screen. Another limitation of the bit-mappeddisplay is the so-called staircase effect in which the diagonal edges oftypographic characters and line art displayed on the screen have ajagged or saw-tooth appearance. The staircase effect can be largelyovercome on gray-scale displays by displaying the pixels that would formnotches in diagonal edges on a bit map display at intensitiesintermediate to the on and off states. The technique, well known asanti-aliasing, is quite desirable because, at any given screenresolution, the legibility of displayed alphanumeric characters appearsto be enhanced, making them look more like the corresponding printedversion.

As is well known to those acquainted with the printing arts, thereproduction of continuous tone pictures (such as photographs) on plainpaper involves the use of a half-tone pattern, a family of small shapes,typically dots or lines typically printed at regular intervals of,usually 50 to 150 per inch.

Half-tone patterns can be produced on the electronic printing device bydividing the page into small, equalsized, rectangular, preferrablysquare areas or cells. Each cell has a cluster of printed dots arrangedwithin it. A small cluster of printed dots corresponds to a light graygray-scale pixel and a large cluster corresponds a dark gray gray-scalepixel. The family of these cells constitutes a set termed hereinafter"super-pixels."

Super-pixels are printed by the line-raster printing device by dividingthe bit map into small sub-arrays, the size of which determines thenumber of different gray-scale values that can be expressed. Forexample, to print images with 64 density levels of gray, a cell orsuper-pixel eight raster lines in height and eight printing dots acrosscan be utilized. Thus, one can provide 64 cells each having a uniquedensity level provided by a respective matrix of dots or points. A lightgray super-pixel can be produced by printing only a few dots inside thecell, whereas a dark gray super-pixel can be produced by printing allbut a few of the maximum possible 64 dots within the cell.

A coding scheme using weighted sets of two-dimensional functions, knownas area character coding, was developed by Altemus and Schaphorst toachieve compression in facsimile transmission, but was apparently notconsidered favorable for gray-scale imagery according to W. K. Pratt,Digital Image Processing, John Wiley & Sons, N.Y., 1978, pp. 705-706.

To simplify the mapping process, each of the different super-pixels canbe assigned a unique super-pixel index number, usually in binary form.For example, a super-pixel index number of 111111 can be assigned to alight gray or white super-pixel and 000001 to a very dark graysuper-pixel. These index numbers can also be used to set the intensityof the CRT screen display, 111111 turning a selected portion of thescreen phosphor on to full brightness and 000001 setting the screenphosphor intensity at that or another portion to almost the minimumlevel. Super-pixel index numbers thus representing the intensity of agray-scale pixel in a picture on the CRT screen can also be used to mapthe appropriate super-pixel within the printing device. Further, thegray-scale super-pixel index number (in the above example) is only sixbits as opposed to the sixty four bits used in the bit map to print theequivalent of the super-pixel. This, in effect, represents a datacompression of better than ten-to-one.

Some electronic typesetters (providing resolutions in excesss of 1000lines per inch) feature so-called half-tone screen generation, i.e.within specified area of a page image, a half-tone picture can beprinted from an array of gray-scale values using a super-pixel scheme.However, when applied to laser printers, the super-pixel scheme is ofonly limited usefulness. In most publishing applications,continuous-tone images are reproduced at resolutions of 50 to 150gray-scale pixels per inch. To reproduce pictures with a resolution of100 gray-scale pixels per inch, super-pixels eight raster lines inheight are required to reproduce pictures with 64 levels of gray. Inorder to print half-tone pictures at a resolution of 100 super-pixelsper inch, a laser printer with a resolution of 800 lines per inch isrequired. This is much higher than that of the inexpensive,currently-available laser printers typically having resolutions in therange of 240 to 400 raster lines per inch. The alternatives, so far,have been the printing of gray-scale pictures with 64, or more, levelsof gray, but at resolutions far less than 100 gray-scale pixels perinch; the printing of pictures at 100 pixels per inch, or higher, butwith far fewer levels of gray than 64; or, most frequently, the printingof pictures at resolutions of less than 100 gray-scale pixels per inchwith less than 64 levels of gray.

When individual copies of documents are to be printed on-demand on alaser printer, each page may be different. If the electronic publishingsystem is be able to print the document at the rated printing speed ofthe printing device, hardware for generating the printer bit map must beable to generate new maps at not less than the printing rate of theprinting device. As the resolution of the printer is increased, the sizeof the map grows as the square of the increase, limiting the on-demandprinting capability of the electronic publishing system. For example, toprint an 81/2×11 inch page, a laser printer with a resolution of 240lines per inch requires a bit map containing 5,385,600 bits. Raising theprinter resolution to 800 lines per inch (needed to print 100 64-levelsuper-pixels per inch) requires a map containing 59,840,000 bits.Reasonably-priced hardware is not currently available to generate such alarge map substantially in real time.

While the use of a gray-scale monitor allows digitized continuous-tonepictures to be seen at full resolution and allows characters and lineart to be seen without the staircase effect, its use makes theelectronic publishing system more complex because separate data basesmust be produced to describe the areas of the page image that are textand that are digitized pictures, and separate maps must be used fordisplay and printing. The need for these separate data bases makes thearrangement and rearrangement of the page images more difficult andslower with any given host computer.

A principal object of the present invention is therefore to provide anovel electronic printing system that permits a high level ofperformance to be achieved at significantly lower cost than has beenpossible with prior art configurations. Yet another object of thepresent invention is to provide such a system that permits the displayof page images containing typographic characters, line art and grayscale pictures, the typographic characters and line art beinganti-aliased for improved legibility.

Other objects of the present invention are to provide such a system inwhich page images may be printed directly and with relatively highresolution from an electronic map used to display substantially the sameimage as an electrooptical display device; to provide such a systemcapable of printing gray scale images with at least 64 gray levels and aresolution of at least 100 super-pixels/inch on line-raster printingdevices with resolutions under 800 line/inch; to provide a system thatincludes an electro-optical display and a graphic printer, which systemis capable of integrating typographic characters and/or graphicsinformation and half-tone screen information, all in a single data basefrom which one may either (or both) print the data out on the printer ordisplay the data on the display; to provide such an electronic printingsystem that requires substantially less working memory to display andprint pages than had been required by prior art electronic printingsystems; and to provide such a novel electronic printing system that isrelatively independent of the printing characteristics of its printer.

To effect these and other objects of the invention, there is provided anovel system for displaying page images including typographiccharacters, graphics and/or gray scale, which system comprises storagemeans containing a set of substantially disjoint index numbers dividedinto two different subsets. The term "disjoint", as used herein, meanshaving no members in common in a set, i.e. every number is unique. Theterm "substantially disjoint", as used herein, is intended to indicate,however, that not necessarily all, but most, of the members of a set areunique.

The first subset of index numbers stored contains gray-scale informationand thus represents a set of gray-scale super-pixels corresponding innumber to the set of levels in the gray scale of the system.

In the present invention, the dots or points in selected cells arearbitrarily ordered to represent one or more shapes embodyinginformation with respect to an edge of a character or graphic form aswell as incorporating a "gray-scale" aspect. Thus, the second subset ofindex numbers includes such information regarding the shape (includingorientation) of an edge and preferably represents a set of another typeof super-pixels (i.e. shape-segments) corresponding to preselectedfragments of typographic characters and line art.

Means are provided for storing an image of the data to be displayed orprinted, as an array of the index numbers ordered in accordance withthose data. Means are also provided for setting the intensity of acorresponding pixel on an electrooptical display screen in accordancewith each of the index numbers stored in the array, and for controllingthe printing of a pattern of dots with a cell to produce correspondinggray-scale super-pixels or shape-segment super-pixels accordingly as theindex number is in the first or second subset. The spatial arrangementof dots in each printed super-pixel embodying gray-scale or edge-shapeinformation is to a large extent arbitrary and is clearly dependent uponthe capabilities of the printing device itself. Thus, it is to beunderstood, in essence, while the gray-scale and edge-shape informationis abstract, the printed embodiment is only an approximation of theabstract information, and that embodiment may be varied according to theprinting equipment employed or improvements made to such equipment.

The system also includes main digital memory means for storing the data(digitized text, line art, pictures etc.) as a plurality ofbinary-encoded words each of the binary-encoded words containing one ofthe index numbers.

The system of the present invention also includes digital-to-analogconversion means connected to the output of the storage means, forconverting a sequence of the index numbers into a sequence ofcorresponding analog signals. Means are included for coupling the outputof the digital-to-analog conversion means to a CRT so as to activateselected pixels of the latter in accordance with the sequence of analogsignals.

In a preferred embodiment of the present invention, the system alsoincludes a video camera for forming photographic images and convertingsame into at least some of the digital data to be displayed by thesystem.

The invention described hereinafter provides, inter alia, not only asystem for electronic editing of a page on a CRT and for printing thatpage substantially as shown, but, in another sense, provides an improveddata compression and decompression system that permits one to bothdisplay and print subtantially the same page of typographic characters,graphics and/or pictures with a considerably reduced amount ofelectronic storage and processing equipment.

Other objects of the invention will in part be obvious and will in partappear hereinafter. The invention accordingly comprises the apparatuspossessing the construction, combination of elements, and arrangement ofparts which are exemplified in the following detailed disclosure and thescope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the presentinvention, reference should be had to the following detailed descriptiontaken in connection with the accompanying drawings wherein:

FIG. 1 is a block diagram illustrating the principal parts of a systemembodying the present invention;

FIG. 2 illustrates several idealized and enlarged typical gray-scalematrices shown as FIGS. 2a-c inclusive;

FIG. 3 illustrates several idealized, enlarged typical micro-shapes orshape-segment matrices shown as FIGS. 3a-e inclusive;

FIG. 4 is an enlargement of an alphanumeric character formed as acomposite array of selected shape-segment matrices; and

FIG. 5 is a graphical representation of a transform curve for the 256states represented by the 8-bit code employed in one embodiment of thepresent invention.

The apparatus of the present invention, as particularly shown in FIG. 1,broadly comprises a system for integrating digital data includingtypographic characters, line art and picture information, selectivelyalternatively or simulataneously to be displayed on a CRT or otherraster scan imaging system, or printed as by a line-raster printer ordot matrix printer. To this end the apparatus of the present inventionincludes central transmission channel means or bus 20 comprising threechannels: control signal channel 22, address signal channel 24 and datasignal channel 26.

The data to be manipulated and reproduced by the system can originatefrom a number of sources. For example, data are typically created asalphanumeric text on a keyboard of a word processor (not shown) thatconverts the text into digital data, or as graphics on the screen of aCRT using, for example, a "mouse" and appropriate software to create thescreen image and convert it to digital data. Such data are fed into thesystem as through serial input port 28, typically an RS-232 port tocentral processing unit (CPU) 29. The latter typically may be an MC68000microprocessor commercially available from Motorola, Inc. of Chicago,Ill., and is coupled to all three channels of bus 20 through CPU businterface 30 that serves as an I/O device to the bus. CPU 29 is alsocoupled, typically by a plurality of parallel data lines 31 and addresslines 32 to CPU memory 33.

Another source of data for the system of the present invention is videosource 34, typically a video camera, the output of which is digitized byanalog-to-digital (A/D) converter 35. Alternatively, source 34 maysimply be a charge-coupled device (CCD) that scans a scene or object andprovides a serial analog output train directly. Means, in the form offrame grabber memory and logic 36, are connected between the output ofA/D converter 35 and all three channels of bus 20 to serve as an I/Odevice to the latter. Frame grabber memory and logic 36 serves to storethe digitized information from video source 34, preferably organizingthat information as data representing individual images or frames. Aframe grabber useful in the present invention is included in the ModelVG-131-06-61 device available from Datacube, Inc., Peabody, Mass. Also,means in the form of sync signal generator 38 are coupled to source 34,converter 35, and memory 36 to insure, as well-known in the art, propersynchronization in the operation of these latter elements.

Yet another important source of data for the system is a main digitalmemory means, such as mass storage 40, for storing data as a pluralityof binary-encoded words or index numbers. Storage 40, for example may beany or all of a floppy disc, hard disc, digital tape storage and thelike, and the usual drive and switching mechanisms for reading the discsor tape. Storage 40 is coupled to all three channels in bus 20 throughanother bus I/O device, mass storage control logic 42, typically aDSD-7215 unit commercially available from Data Systems Design of SanJose, Calif. Logic 42 serves to transfer data and other signals in acontrolled manner between bus 20 and mass storage 40 when desired.

Other I/O devices are coupled to bus 20 for transferring data, controland address signals used in converting data into images by the system,and are shown as video bus interface 50 and printer bus interface 52.I/O devices are coupled to bus 20 for moving data for ultimateconversion to an image, either printed or displayed, and are shown asprinter line buffer means 51 and page image memory 53. Interfaces 50 and52 are coupled to all three signal channels in bus 20, while printerline buffer means 51 is connected to an output from printer businterface 52.

Interface 50, intended to accept control, address and data signals fordisplay of the latter on a device such as a CRT, has its outputconnected to memory and timing logic 54, the operation and structure ofwhich will be described hereinafter. The output of the logic 54 iscoupled through data line 56, address line 57 and control line 58 tocorresponding input terminals of page image memory 53. The latter,typically a random access memory (RAM), is organized for storage of, forexample, 10⁶ 8-bit bytes of data from channel 26. Output connectionsfrom RAM 53 (for example, in the form of 128 parallel lines representing16-pixels) are coupled to corresponding inputs of shift register means62. Clock line 64 is connected between an output from logic 54 and theclock terminal of shift register means 62 to provide the necessary syncsignals to the latter to insure proper timing in its operation. Theoutput of shift register means 62 in turn is connected to the input of asecondary memory or CRT look-up table, typically in the form ofpreloaded read-only-memory or ROM 66. The output of ROM 66 is coupledthrough digital-to-analog (D/A) converter 68 to the intensity controlinput of an electro-optical display device such as CRT display 70. Videosync means 71 are appropriately connected to logic 54 and A/D converter68 and display 70 for controlling operation of the latter. If one wishesto provide more flexibility to permit use of different types of CRTs,one may employ a RAM in place of the ROM 66, the CRT look-up table beingin such case loaded into the RAM on command from bus interface 50.

The output of buffer means 51 is connected to an input of the M (or mostsignificant bit) address register 76. Buffer means internally cancomprise a demultiplexer feeding a pair of parallel printer linebuffers, each of which has a typical capacity of 1000 bytes, the outputof the line buffer being then fed into the input of a multiplexer.

Printer bus interface 52 has its output connected to the input ofcontrol register means 78 in which the printer address and printercontrol signals passed by interface 52 are stored. Outputs from registermeans 78 are connected to buffer means 51 and to L (or least significantbit) address register 80, so that buffer means 51 and register 80 arecontrolled by appropriate signals from register means 78.

The outputs from address registers 76 and 80 are connected to the inputof address counter 82, the output of the latter being connected to theinput of printer look-up memory 84. The latter is provided typically inthe form of a preloaded read-only-memory (ROM). A control input to ROM84 is connected to an output from interface 52. The output of ROM 84 isconnected through shift register 86 that converts a parallel signaloutput from ROM 84 into a serial signal train for introduction into thedata input terminal of printer 88. If one wishes to endow the systemwith more flexibility to accomodate for different types of printers, itmay be desirable to provide memory 84 in the form of a random accessmemory (RAM) rather than as a ROM. In such case, the matrix information,instead of being prestored in memory 84 as hereinafter described, shouldbe loaded on command into the RAM through an appropriate connection frombus interface 52.

Printer timing control means 90 is provided, its inputs being connnectedto outputs from interface 52, register 78 and printer 88 so as to acceptcontrol signals from the latter. The outputs of printer timing controlmeans 90, in turn are connected to appropriate control input terminalsof register 86 and printer 88 so that the latter are controllable bysignals from timing control means 90.

For purposes of the present invention, the data are organized forprinting as either gray-scale cells or matrices or shape-segment cellsor matrices as hereinafter described. Each matrix is preferablyorganized as an n×m cell of binary values, and a preferred form is an8×8 cell. All examples hereinafter given will be based upon the 8-bitformat, but other numbers of bits, such as 6, 10 or the like, may alsobe used depending on the total number of states one wishes to represent.The use of 8-bit binary values permits one to define 256 states. Ofthese, the first 64 states (i.e., those represented in sequence bybinary numbers from 00000000 to 00111111) may be used to representcorresponding unique gray-scale values. The 64 gray-value matrices areeach a square 8×8 cell of binary-valued numbers that can also bedescribed in terms of the corresponding physical analog i.e. black orwhite elements. Such cells will then range from one which has no blackelements to one which has no white elements, the black elements for allintermediate-valued cells being preferably in a distribution weightedmost heavily to clump the black elements substantially centrally in eachcell (or distribute the white elements toward the periphery of thecell), thus creating, for the 64 matrices, a series in which the singlecenter dot of the lightest gray level appears to expand in size from aminute element to a large composite center to a completely filled cell.For example, there is shown in FIG. 2 a number of representativegray-scale matrices, of which the cell at FIG. 2a contains only 4 blackelements, the latter being are distributed centrally in the cell. InFIG. 2b, the cell is shown with 32 black elements of the total 64.Again, the elements in FIG. 2b are centrally distributed. In the yetdarker cells as exemplified by FIG. 2c where 60 of the 64 elements areblack, the white elements are distributed peripherally.

Each of these gray-scale matrices are prestored in the form of eight8-bit binary bytes in a look-up table in printer memory 84. Each suchmatrix is addressed in storage by the corresponding last 6 bits of thesequence of the first 64 8-bit binary numbers of the data. For example,the address of the matrix with no black elements (or all binary ones)may thus be 000000. The matrix formed of half binary ones and halfbinary zeros is similarly addressed at 011111. One may use binary valueswith larger numbers (such as 16) of bits each, for example if one wishesnot only to establish a gray-scale with a larger number of levels, alsoto do so in a plurality of colors.

Of the 256 states identifiable by an 8-bit binary number, the first 64are used as above-described as addresses for 64 corresponding uniquegray-scale matrices stored in memory 84, and the remaining 192 numbersof the 256 are then used to address predefined shape-segment matrices.The shape-segment matrices are preferably defined by an arrangement(typically 8×8) of binary numbers prestored in another look-up table inmemory 84, but in such shape-segment matrices the same binary values orelements are grouped contiguously and non-centrally, thereby to define amicroedge or shape. For example, there is shown in FIG. 3a a matrixdefining a vertical straight edge disposed two bits from the left matrixmargin. In FIG. 3b there is shown another straight edge, but disposedhorizontally four bits from the top matrix margin. In FIGS. 3c and 3dthere are shown two matrices with diagonal edges ascending withdifferent slopes to the right. FIG. 3e shows a matrix with an irregularedge. In the preferred embodiment of the invention there are selectedand prestored 192 different shape-segment matrices of the type hereindescribed, each addressed by the second sequence of 192 binary numbers.

By combining or assembling selected ones of these 192 differentshape-segments, one can define image edges of any desired curvature oftypographic characters or a graphic line on the CRT or on the printer.Consequently, stored in mass storage 40 are preferably a plurality offonts of typographic characters, each of which is in the form of anarray or assemblage of shape-segment matrices identified, in massstorage 40, by a set of the respective addresses to memory 84. Forexample, in FIG. 4 there is shown the letter "C" formed of a pluralityof edge sets (here 4×4 matrices for ease in illustration).

The second sequence of 192 binary addresses also constitutes additionaladdresses of values prestored in memory 66. Those prestored values inmemory 66 at such addresses each represent a linear transform into acorresponding intermediate gray level that is used, as will be describedhereinafter, to provide anti-aliasing in images formed on CRT 70.

The use of such gray-scale and shape-segment matrices endows the presentinvention with flexibility by avoiding the usual requirement ofemploying substantially disjoint bit maps to represent characters on theCRT and the printer, and permits one to define both video images andtypographic characters in terms of these stored matrices.

In operation, to form and reproduce a video image either or both on avideo display screen or in printed form, as is well known in the art, acontinuous image is scanned by video source 34 and is sampled in thespatial domain to produce an ab array (or frame) of discrete samples,typically 640×480. The samples are then quantized in brightness (orintensity) by using 2^(K) levels to produce a serial signal train withabK bits per frame. The bits are organized into K-bit bytes, each ofwhich represents the corresponding light intensity of each image-elementread in sequence during a raster scan of the imaging device, whether thelatter is a video camera or a CCD. The sequence of intensity values inbinary form is stored in frame grabber memory 36 until the next verticalsync pulse from generator 38 indicates the end of a frame. The framegrabber operates so that if a signal has not been received from theoperator to preserve that frame, the next frame replaces the previousframe. When an appropriate signal is received from the operator, theframe in memory is frozen and storage of subsequent video frames isinhibited.

Data introduced into port 28 is typically in an ASCII string of 8-bitbytes, each of which represents either a typographic character or acontrol symbol. These bytes are stored in the memory of CPU 29. Memory33 should have, inter alia, sufficient storage to accept a desirednumber of currently available applications programs that the designerwishes to run on the system of the present invention, for example,typesetting, layout, word processing, graphics, generation, and thelike. A particular stored program provides byte mapping, and under thecontrol of such a program, byte maps of various fonts of typographiccharacters can be preprepared and stored in mass storage 40 ashereinafter described, each character being addressed by a correspondingbyte originally representative of the ASCII character.

Upon command of the operator, these digitized signals representing thefrozen frame, or the binary digits in the byte maps, may be transmittedas a serial train of such bytes (here K=8) from frame grabber memory 36or storage 40 as the case may be, to memory 53 and from memory 53 as aparallel output of sixteen bytes. The output of memory 53 is fed toregisters 62 to adjust timing and transform the parallel byte input backinto a serial byte train. This latter output is fed into look-up table66 where the last 6 bits of each 8-bit byte serve as an address for acorresponding gray level value. While one could convert the 6-bitadresses directly to analog values for display, it is preferred to gothrough the look-up table because the relation between the intensityvalues recorded by the camera and what one wishes to reproduce may notbe the same or even linearly related. Thus, there is prestored in memory66 a sequence or array of substantially disjoint index numbers ordigital values, each representing, when converted by digital-to-analogconverter 68 into a corresponding analog voltage, an excitationintensity of the phosphors of CRT 70 along a first gray scale intypically equal increments over a first dynamic range from zero to fullintensity. The 64 index numbers, here 8-bit binary values, selected torepresent the gray-scale of the printing system then constitute therespective addresses of the first gray-scale values stored in memory 66.Thus, upon applying the 8-bit binary numbers from shift register 62 tothe input of memory 66, it will be seen the output of memory 66 will bea series of 6-bit (minimum) binary digits which, when converted tovoltages, will control the CRT excitation across the desired firstgray-scale of 64 levels. The remaining substantially disjoint 192 indexnumbers or binary addresses for shape-segment matrices stored in memory84 for the printing system, are here used as addresses for a second setof gray-scale values across a second dynamic range, the latter beingmuch lesser than the first dynamic range of the first gray-scale. Thesecond gray-scale is used to alter image edges on CRT 70 at gray levelsthat provide anti-aliasing. The transform curve for the 256 states oraddresses and the corresponding values stored in memory 66, is shown inFIG. 5 wherein the addresses 0 to 63 (binary) represent the firstgray-scale values, and the addresses from the binary representation ofdecimal 64 to the binary representation of decimal 255 represent aplurality of lesser increments of gray-scale over a reduced dynamicrange.

The array of binary numbers from table 66, representing the dataobtained from video source 34, when transmitted for display on CRT 70,are converted directly by D/A converter 68 to corresponding analogvalues, each of which represents an intensity level at which acorresponding phosphor dot on the screen is excited. Thus the videosystem converts to an array of digital values, the analog levels of animage read by video source 34, manipulates or alters the array of thosedigital values to achieve desired changes in the image, and reconvertsthose changed digital values back into analog values for display on a TVmonitor or CRT. With respect to typographic characters or graphicsinformation, the video system is addressed by binary numbers that in theprinting portion of the present invention are addresses forshape-segment matrices, but in the video portion of the presentinvention represent a sequence of CRT excitation values across arelatively small or second, third, etc., dynamic ranges (such as areshown in FIG. 5), which values are stored in a look-up table.

When one wishes to display a typographic character or a graphic line onCRT 70, from a particular font stored in storage 40 the binary addressesof that particular sequence of shape-segment matrices used in thatcharacter or line are fetched, being then sent on to look-up table 66.At the latter, the sequence of levels (in binary notation) correspondingto the sequence of addresses is provided and forwarded to converter 68.

The output from converter 68 is fed to CRT display 70 where a rasterdisplay of those levels as excitation voltages for the screen phosphorwill create the desired image of the selected typographic character. Theimage displayed on the screen can then be manipulated as desired, forexample, cropped, rotated, shifted, or its contrast and overallbrightness altered. Depending on the nature of the applications programspreferably stored in memory 33 or mass storage 40, the image can also behighlighted, painted, or erased in part or whole. The system preferablyincludes means for selecting a desired area on the display of the pagebeing worked on, and permitting the operator to select and move to a newlocation all or part of that selected area. These steps are accomplishedsimply by identifying those index numbers that correspond to theselected area, rearranging those index numbers to shift the area acrossthe display to the new location, the rearranged array of index numbersthus being stored in place of the original array. All such knownoperations, the details of which are here not pertinent, are achieved inaccordance with the applications programs operating on the data storedin memory 53, the ultimate result of such operation being shown,substantially in real time, on the CRT. Thus, when operator has achieveda modified video image, as desired the information representing thatmodified image is stored both in page image memory 53 in ordered formand in duplicate in mass storage 40.

It will be apparent that while simply converting the digital value ofthe binary numbers to corresponding analog values will suffice toprovide a CRT image with a 64-level gray-scale, this technique will notprovide adequate information to permit one to form an image on a"gray-scale" of only 2-levels as provided by a typical printer. Thus, inthe present invention, each of the 8-bit numbers employed as addressesto the first gray-scale values of maximum dynamic range stored in table66, are also used as addresses to a plurality of gray-scale super-pixelsor gray-scale matrices stored in memory 84. Typically, each suchsuper-pixel will be about or less than 0.01 inches in height and inwidth, so is well below the normal limit of resolution of one's eye.

To these ends, the video data and/or the typographic information, as itmay have been modified and stored in both memory 53 and mass storage 40,are placed on line 26, usually as a series or sequence of 8 parallel-bitbytes, and transmitted to buffer means 51 and printer bus interface 52.It should be remembered that each such byte represents the address ofeither a corresponding shape-segment matrix or a gray-scale matrixstored in memory 84. As noted hereinbefore, buffer means 51 preferablyis a double line buffer which serves to adapt the timing of the signaltransmission rate to one suitable for use in the printing system. Theoutput of buffer means 51 is fed to address register 76 that stores andshifts out only the sequence of bytes representing the first row orhorizontal line of the character to be printed. A command as to how manylines are in each matrix to be printed is loaded through interface 52into register 78. The output from register 76 is fed into addresscounter to provide the identification or sequence of addresses for therequisite gray-scale or shape-segment matrices to be fetched from memory84. The first lines of each of these matrices, in sequence, are thenfetched from memory 84, shifted into a serial train in register 86 andprinted out as a line of two-valued intensity dots on printer 88. Theaddress counter is then incrementd by one by register 80 and the secondlines of each of the selected matrices are then printed in sequence in aline of dots below and in register with the first line of dots. Counter82 is incremented by one until the complete number of lines (typicallyeight) required to print each complete matrix, has been completed. Atthis point, register 76 loads the sequence of addresses of the next rowof matrices to be printed and the operation is repeated with the newmatrices. This operation is required because the printer is usuallyunable to print each matrix simultaneously but must do so in terms of asequence of lines of dots.

While for convenience in exposition the formation of gray-scalesuper-pixels and shape-segment super-pixels by a printer has beendescribed in terms of points or dots, it is to be understood that theinvention is not limited to any particular form of dots. For example,while the dots are desirably minute geometric shapes, they can assumeany geometric form, regular or irregular, for example, circles,diamonds, squares, lines, blotches, or the like. In a preferredembodiment, the printer is a laser, line-raster type printer aspreviously described, and the cells or super-pixels formed by theprinter typically are two or more raster lines in height. In such case,the cells are printed by turning the laser on and leaving it on, forexample for a predetermined multiple of a base time period, thereby toprovide a variable-length, raster line segment that is equivalent to amultiple of a number of contiguous dots. In essence, then, the "dots"are essentially rendered as contiguous exposures provided by themultiple of the time period during which the laser excites thephotosensitive surface to which it is directed. The maximum line segmentprovided in such case should not be greater than the length of the cell.In other words, the length of the pixel should equal or exceed themaximum segment produced by the laser operated over the largest timemultiple represented by a binary index number.

It will be appreciated that while the significant information in a fontcharacter is printed out from shape-segment matrices having a number ofblack dots therein, the background of the character in fact is usuallywhite, and that portion can be represented by the "all-white" matrixwhich may serve a dual function as a gray-scale matrix and ashape-segment matrix, as may the "all-black" matrix.

In displaying typographic characters and the like on the CRT, theshape-segment addresses are translated into excitation voltages acrossthe smaller dynamic range, and the use of these medium grays to form theedges of the displayed charcter, blur or fill in the relatively sharpstaircase effect that would otherwise occur, thereby providing effectiveanti-aliasing.

Since certain changes may be made in the above apparatus withoutdeparting from the scope of the invention herein involved, it isintended that all matter contained in the above description shall beinterpreted as illustrative and not in a limiting sense.

What is claimed is:
 1. A system for displaying on electro-opticaldisplay means and/or for printing on printing means typographiccharacters, line art and pictures, said system comprising:means storingan image as an array of a first subset and a second subset of a set ofsubstantially disjoint index numbers, each of said numbers of said firstsubset representing information corresponding to a respective densitylevel in a gray scale, each of said numbers of said second subsetrepresenting information corresponding to a unique shape of an edge;means for converting at least a major portion of said array into adisplay of substantially said image on said electro-optical displaymeans; and means for converting at least a major portion of said arrayinto printed form on said printing means.
 2. A system as defined inclaim 1 wherein said index numbers are multiple-bit binary numbers.
 3. Asystem as defined in claim 2 wherein all of said multiple-bit binarynumbers have a predetermined, fixed length of n bits.
 4. A system asdefined in claim 3 wherein n=8.
 5. A system as defined in claim 3wherein n=16.
 6. A system as defined in claim 1 includingmemory meansstoring said set of disjoint index numbers, wherein each of said numbersof said first subset represents each said density level rendered as arespective matrix of points forming a gray-scale cell to be printed bysaid printing means, each of said numbers of said second subsetcorresponding to a unique shape segment rendered as a respective matrixof points to be printed by said printing means; and means for definingsaid array in terms of said index numbers.
 7. In a system as defined inclaim 6 wherein each said index number represents a cell formed ofportions of at lest two successive lines of the raster provided by saidprinting device.
 8. In a system as defined in claim 7 wherein saidprinting device is a laser printer for forming an image on aphotosensitive surface.
 9. A system as defined in claim 7 wherein thewidth of each of said cells is equal to the pitch of said raster linesmultiplied by the number of raster lines included within each cell. 10.A system as defined in claim 6 wherein said printing device is of thedot matrix-type and each index number of said array corresponds to aunique matrix of dots to be printed by said device.
 11. A system asdefined in claim 10 wherein said matrix is square.
 12. A system asdefined in claim 6 wherein each said density level corresponding to therespective members of said second subset of index numbers is so selectedthat said shape segments can be combined to create antialiasedtypographic characters and graphics.
 13. A system as defined in claim 12including a look-up table for storing a plurality of index numberscorresponding to unique density levels of said cells, said index numbersconstituting addresses in said look-up table for corresponding ones ofsaid density levels.
 14. A system as defined in claim 1 wherein theoptical resolutions provided by said display means and by said printingmeans are different.
 15. In an system for the altering and subsequentprinting of a page, said page containing typographic characters,graphics, and/or pictures, wherein said alteration is performed with theaid of an electro-optical display means and such altered page is printedon printing means, the improvement comprising:means storing a set ofsubstantially disjoint index numbers in two subsets, each of saidnumbers of said first subset representing a unique density levelprovided by a respective matrix of points forming a gray-scale cell tobe printed by said printing means, each of said numbers of said secondsubset corresponding to a unique shape segment to be printed by saidprinting means; means for converting selected numbers of each of saidsets into an array corresponding to an image of said page on saidelectro-optical display means; means for converting at least a majorportion of said array into said gray-scale cells and shape segments soas to print said page on said printing means; means for selecting adesired area of a page shown on said display means; means foridentifying the index numbers corresponding to said desired ara; meansfor selecting a new location for said desired area on said page; meansfor rearranging the identified index numbers within said array so thatsaid desired area appears at said new location; means for altering indexnumbers within said first set of index numbers so as to alter the tonescales of a picture included within a page being displayed on saiddisplayed means; and means for printing said gray-scale cells and shapesegments in accordance with the respective rearranged and altered indexnumbers so as to form a printed page.
 16. In apparatus for providing aprinted page containing typographic characters, graphics, and/orpictures, the improvement comprising:a printing device of thelinear-raster type; means storing a set of substantially disjoint indexnumbers in two subsets, each of said numbers of said first subsetrepresenting a unique density level provided by a respective matrix ofpoints forming a gray-scale cell to be printed by said printing device,each of said numbers of said second subset corrsponding to a uniqueshape segment to be printed by said printing device; means forconverting selected numbers of each of said subsets into a sequence ofvariable-length portions of the raster lines provided by said printingdevice, said portions approximating respective shape segments andrespective gray-scale cells; and means for printing each said rasterline portion on said printing device so as to form said printed page.17. In apparatus as defined in claim 16 wherein said sequence of rasterline portions is rendered in terms of multiples of a base time period,groups of said portions apparoximating respective shape segments andrespective gray-scale cells, the multiple of said time period per pixelexceeding the length of the binary number representing each said cell.18. In a system for displaying on a linear-raster imaging device and forprinting on printing means tyographic characters, line art and/orpictures, the improvement comprising:means storing an image as an arrayof a first subset and a second subset of a set of substnatially disjointindex numbers, each of said numbers of said first subset representinginformation corresponding to a respective density level in a gray scale,each of said numbers of said second subset representing informationcorresponding to a unique shape of an edge; means for converting atleast a major portion of said array into a display of substantially saidimage on said linear-raster imaging device; and means for converting atleast a major portion of said array into printed form on said printingmeans.
 19. In a system as defined in claim 18 wherein said array isformed of a plurality of like sized sequences of said index numbers,each of said sequences corresponding to a respective raster lineprovided by said imaging device, each of said index numbers in eachsequence representing the intensity level of sequential portions of thecorresponding raster line.
 20. In a system as defined in claim 19wherein said imaging device comprises a cathode ray tube.
 21. In asystem for displaying on elctro-optcial display means and for printingon a linear-raster printing device typographic characters, line artand/or pictures, the improvement comprising:means storing an image as anarray of a first subset and a second subset of a set of substantiallydisjoint index numbers, each of said numbers of said first subsetrepresenting information corresponding to a respective density level ina gray scale, each of said numbers of said second subset representinginformation corresponding to a unique shape of an edge; means forconverting at least a major portion of said array into a display ofsubstantially said image on said electro-optical display means; andmeans for converting at least a major portion of said array into printedform on said printing device.